The ryanodine receptor is a calcium release channel localized to the internal membrane system in muscle and neurons. Three isoforms of the ryanodine receptor have been described in chicken: two skeletal muscle forms termed alpha and beta and a cardiac muscle form. The distribution of the ryanodine receptor was mapped in developing chicken brain using two monoclonal antibodies (Mab). Mab110F recognized the alpha skeletal muscle form exclusively and Mab110E recognized both the beta and cardiac forms but not the alpha form. In the developing and adult chicken brain, only cerebellar Purkinje neurons contain the alpha ryanodine receptor while neurons throughout the rest of the brain contain the beta/cardiac form. In the adult, little immunolabeling for the beta/cardiac form was seen within Purkinje neurons. However, the distribution of the beta/cardiac form changed during the first post-natal week. Whereas in the embryonic cerebellum, the beta/cardiac form was localized prim arily within Purkinje neurons, the amount of labeling within Purkinje neurons gradually decreased during the first post-natal week while a fine, punctate labeling began to appear in the molecular layer. To determine whether these profiles were indeed the presynaptic boutons of parallel fibers, 1-2 um thick sections of cerebellum were cut in the coronal orientation and examined at 400 keV using IVEM. In this orientation, the parallel fibers are running in a longitudinal direction. Using IVEM, the punctate labeling was seen to be associated with varicosites contained within longitudinal stretches of fibers of the same size and morphology as parallel fibers, providing further evidence that the beta/cardiac form is localized within presynaptic boutons of parallel fibers. This was one of the first anatomical demonstrations that nerve terminals contain calcium channels capable of mobilizing calcium from intracellular stores. This research formed part of Dr. Ouyang's doctoral dissertation. A manuscript detailing this work was published in Ouyang et al. Brain Res., 775: 52-62, 1997.